1. Field of the Invention
The present invention relates to linear light valve arrays having transversely driven electro-optic gates and to a method of making such arrays.
2. Description of the Prior Art
One form of light valve comprises a gate that is electrically addressable for changing the polarization of light. The gate is sandwiched between a polarizer and a crossed analyzer. The gate generally is made of a sheet of transparent material exhibiting an electro-optic effect. Such a material is lanthanum doped lead zirconate titanate (PLZT), on which is provided a pair of electrodes for establishing an electric field in the material to stimulate the electro-optic effect.
In many applications, an array of light valves is needed. In one such light valve array, a sheet of PLZT material has a plurality of coplanar interleaved electrodes formed on one surface of the sheet generally normal to incident plane polarized light, thereby defining a plurality of light valve gates on the sheet. The selective application of voltages to adjacent electrodes establishes an electric field in the PLZT material. This field has a component generally perpendicular to the direction of incident light. The incident light is typically polarized at a 45.degree. angle with respect to some component of the applied field. The electric field causes the PLZT material to become birefringent thereby changing the state of polarization of incident light. As a result, the transmission of light through the analyzer varies as a function of the strength of a transverse component of the electric field in the light valve. Therefore, by varying the applied voltage, the intensity of light can be modulated. For an example of such a light valve array having coplanar electrodes, see commonly assigned U.S. Pat. No. 4,229,095 to Mir. A difficulty with a light valve array having coplanar electrodes is that a voltage signal applied across coplanar electrodes of a gate is inefficient in producing components of electric field perpendicular to the incident light throughout the volume of the gate. Consequently, relatively high applied voltages are required to operate such light valve array gates.
In another approach, U.S. Pat. No. 3,873,187 to Brooks discloses a linear array provided with transversely driven electro-optic gates. FIG. 1 depicts such an arrangement wherein a light valve array 10 has spaced electro-optic gates 12. Metallized addressable electrodes 14 are provided on opposite parallel surfaces of each gate. Except for the end gates of the linear array, each gate electrode 14 is electrically connected to another electrode of an adjacent gate. Plane polarized light is shown to be incident upon surface 12a and passes through a gate 12.
Each gate 12 is a rectangular, parallelepiped of electro-optically active material, mounted in line (linear) on a substrate 16. When a voltage is applied across gate electrodes, an electric field is established transversely across the distance t of the gate 12 generally perpendicular to the direction of propagation of light through the gate. The input light is propagated along an axis shown by line 15. This axis is perpendicular to the established electric field and to the receiving surface 12a. Light which was initially plane polarized at a 45.degree. angle (shown as line 17) to the direction of the field E--E in the electro-optic material travels a distance L through a gate 12. Since the electric field produced in a gate is uniform throughout the gate's volume, a gate can be operated at a relatively low voltage. In making such light valves, however, difficulty is encountered in forming and filling the grooves with metal for the electrodes 14 especially if the spacing between gates in the array is small. Another problem with the manufacture of FIG. 1 light valve arrays is that of making electrical contact with the electrodes of each gate. As shown in FIG. 3 of the above-described Brooks patent, a fine wire is strung through the grooves defining each gate prior to filling the grooves with a conductive metal material. The wires are then bonded to a circuit on which the electro-optic material is mounted. The stringing (of fine wire), the filling, and the bonding steps are time consuming. Light valve arrays produced by this method also may not be reliable.
A further problem with the transversely light valve array shown in FIG. 1 is that each gate electrode is shared by two adjacent gates. As a result, the scheme for addressing the light valve array is relatively complicated since each gate's electrodes are not discretely addressable. If the gates are operated in exclusive-or fashion, it is difficult to implement pulse width modulation techniques since each time a light valve changes its state, a ripple effect is triggered changing the state of adjacent gates. Also, it is difficult to maintain the spacing between electrodes of each gate. This spacing can change from gate to gate since the design is susceptible to groove cutting errors. If a gate has a different dimension t, the established electric field in such gate will vary from some desired value.